1. Field of the Invention
This invention relates to an antibody against hemagglutinin of human influenza A virus, a polypeptide containing an antigen site recognized by the antibody, and a gene coding for said polypeptide.
2. Description of Related Art
There are three types (A, S and C) of influenza viruses and the worldwide prevalence of influenza causing a large number of deaths is caused by human influenza A virus.
Influenza A virus is further classified into various subtypes depending on the antigenicities of hemagglutinin (hereinafter referred to simply as HA) and neuraminidase (hereinafter referred to simply as NA) which are vital surface proteins. There have been known so far three subtypes of human influenza A viruses, namely, the H1N1, H2N2 and H3N2 subtypes.
The HA of influenza A virus comprises two structurally distinct regions, namely, a globular head region and a stem region. The globular head region contains a receptor binding site which is responsible for virus attachment to a target cell and participates in the hemagglutination activity of HA. On the other hand, the stem region contains a fusion peptide which is necessary for membrane fusion between the viral envelope and an endosomal membrane of the cell and thus relates to fusion activity [Wiley et al., Ann. Rev. Biochem., 56, 365-394 (1987)].
All of anti-HA antibodies, which have been obtained hitherto as an antibody capable of recognizing the H1N1 and H2N2 subtypes, recognize the globular head region of HA. However, this region most frequently undergoes antigen mutation. Therefore, these antibodies are not common to the subtypes of human infleunza A virus and, further, lose the recognizing ability with antigenic changes in the HA of the virus.
On the other hand, Green et al. have synthesized a polypeptide based on an amino acid sequence in the stem region of HA of the H3N2 subtype and obtained antibodies against this polypeptide. However, these antibodies have a low neutralization activity (Published Japanese Translation of PCT Patent Applications from Other Countries, No. 501714/1984). Furthermore, the polypeptide per se employed as an antigen does not react with rabbit antiviral serum obtained by immunizing with the H3N2 subtype, which suggests that there is a problem from the viewpoint of antigenicity too [Cell, 28, 477-487 (1982)].
The infectivity of the HA of influenza A virus is activated when the HA is cleaved at one site with a protease. The larger polypeptide thus obtained is called HA1 while the smaller one HA2. It is believed that between these polypeptide HA2 will undergo less antigen mutation due to the subtype.
In East German Patent Laid-Open No. 228737, H. Glathe et. al. describe that HA2 is taken out by treating viral particles successively with an acid and trypsin or with a reducing agent alone.
By these treatments, however, HA molecules are destroyed in the stereostructure and irreversibly denatured. As a result, the HA2 thus obtained does not have its inherent stereostructure. In addition, the above-mentioned patent is silent whether the efficacy of the obtained HA2 as a vaccine has been specifically confirmed or not.
Human influenza A virus periodically changes types of HA and NA and thus causes wide prevalence. It is often observed that vaccinization before winter, i.e, the season of prevalence, produces no effect, since the prevalence is caused by a virus of a different type. If an antibody, which is common to virus subtypes in HA and NA molecules and capable of recognizing an antigen site hardly undergoing antigenic mutation, in particular, the configuration, and has neutralization activity for viruses, can be acquired, this antibody is usable in the diagnosis, prevention and treatment of infection with the A virus. Furthermore, the antigen site per se is useful as a vaccine.